<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Tomatoo and display</title>
    <style>
        *{
            margin: 0px;
            padding: 0px;
        }
        .tudou{
            position: relative;
            width: 444px;
            height: 320px;
            margin: 30px auto;
            background-color: #ff8500;
        }
        .mask{
            display: none;
            position: absolute;
            width: 100%;
            height: 100%;
            background-color: rgba(0,0,0,.2);
        }
        .tudou:hover .mask{
            display: block;
        }
    </style>
</head>
<body>
<div class="tudou">
    <div class="mask"></div>
</div>
</body>
</html>